This is a wierd but true thing. As you know from the basic interval theory and also from your own experiences, most commonly used interval progressions are I, IV and V which means notes or chords along the Root, Perfect Fourth and Perfect Fifth. The note between the Perfect Fourth and Perfect Fifth is called Augmented Fourth or Diminished Fifth or also called as the Tritone.
If you take G, then the perfect fourth is C and perfect fifth is D and the tritone is C#.
NOTE: Before you read further, remember the contents could be disturbing, so if you are one of those thin hearted, close the browser immediately and go home and drink milk. And also rep me for saving your life just in time.
This interval has a disturbing effect to the brain and also quite evil to other beings as well as plants. In ancient days, this was called as a devil's interval and it went as far as to even ban this interval from being played in churches. This was also thought to be played by Devil in Hell. Musical Punishment, I guess . This was also enough justification and reason for a lot of metal bands that began using this. Even now, your traditional band and straight forward band never uses it. The same note could figure in whenever a chromatic run or as an incidental note but usually gets avoided being played on the same intervallic difference.
Flat Fifth Power Chord ......
R = Root, b5 = Flat Fifth or Augmented Fourth or Tritone, P5 = Perfect Fifth
5th Power Chord = R + P5
Flat Fifth Power Chord = R + b5
Play this Flat Fifth power chord and hear for yourself as how disturbing it sounds. It wont sound pleasant obviously. It's meant to be bad, wicked and evil.
Flat Fifth Progression .......
Lets take a chord progression of power chords for some Rhythm playing. I am not even going to tell you about the strumming pattern or timing. It's all on your own choice.
G - C# - G
C - F# - C
Try these two evil progressions.
These are just the basics and you could take it as far as your imagination can take you. You could take your Major or Minor chords and replace the fifths with the flat fifths and hear this "Home Made Evil".
Finally, after you go home and play this, dont blast me because you got pissed off, someone at home fell sick, your dog started howling and your brother points a cross at you anytime he sees you.
Anyway, you needn't use this, at least it's a knowledge you could be aware of.